1. Field of the Invention
The present invention relates to a liquid crystal display technique.
2. Description of the Related Art
A liquid crystal display employing a particular display mode such as in-plane switching (IPS) mode, vertically aligned (VA) mode and optically compensated bend (OCB) mode can achieve high response speed. Even such a liquid crystal display, however, still has not achieved a response speed comparable to that of a cathode-ray tube (CRT) display.
JP-A 2005-202390 (KOKAI) and JP-A 2008-112021 (KOKAI) describe a liquid crystal display utilizing Kerr effect. Kerr effect is the effect of a transparent isotropic medium to exhibit an anisotropic refractive index at a magnitude in proportion to the square of an external electric field. A liquid crystal material exhibiting Kerr effect achieves a fast electric field-response of several milliseconds or less because a correlation length of liquid crystal molecules is short.
As a liquid crystal phase exhibiting Kerr effect, the so-called blue phase is known. The blue phase is, for example, a phase that appears within a temperature range between those for the cholesteric phase (chiral nematic phase) and the isotropic phase.
As the liquid crystal material exhibiting the blue phase, a liquid crystal phase capable of exhibiting the cholesteric phase is used. For this reason, similar to a liquid crystal material exhibiting the cholesteric phase, a liquid crystal material exhibiting the blue phase is seen colored due to a selective reflection. Since this color is typically blue, in the case where a liquid crystal display is so designed that the liquid crystal material exhibits the blue phase when displaying a black image, it is possible that the black image is seen bluish. In addition, this coloring hinders achieving a high contrast ratio and a wide viewing angle. In particular, the influence of the coloring becomes significant when the display is used under strong light of the outdoor environment or when the brightness of the backlight for illuminating the display is lowered.
In this regard, JP-A 2005-202390 (KOKAI) describes that the chiral agent content of the liquid crystal material is increased to make the selective reflection wavelength shift from the visible region to the ultraviolet region. When the selective reflection wavelength is within the ultraviolet region, the coloring due to the selective reflection cannot occur. Therefore, it is possible to prevent the above-described problems from occurring.